Document images which are scanned using 8 bits per pixel require large amounts of storage space and expensive hardware for processing. Scanned documents are currently quantized using one bit per pixel, which reduces the hardware and processing requirements, but degrades the image quality, specifically when these images are displayed on display devices which support 4-8 bits per pixel
One known method of quantizing document images in a single-bit down is to use one-bit adaptive thresholding as disclosed in U.S. Pat. No. 5,583,659, entitled "A Multiwindowing Technique For Thresholding An Image Using Local Image Properties," issued Dec. 10, 1996, to Y. Lee, J. Basile, and P. Rudak. This approach limits the display to one bit. The current method of quantizing document images in a multi-bit domain employs fixed threshold points for each gray value. This approach results in poor image quality when a small number of bits per pixel is used to reduce data storage and processing requirements. There is a need therefore for an improved method of quantizing document images to optimize image quality when displayed on a multilevel display device while minimizing data storage requirements.